1 files changed, 54 insertions, 0 deletions
diff --git a/users/sterni/nix/flow/default.nix b/users/sterni/nix/flow/default.nix
new file mode 100644
index 000000000000..838e65bfb20e
--- /dev/null
+++ b/users/sterni/nix/flow/default.nix
@@ -0,0 +1,54 @@
+{ depot, ... }:
+
+let
+
+  inherit (depot.nix)
+    yants
+    ;
+
+  # we must avoid evaluating any of the sublists
+  # as they may contain conditions that throw
+  condition = yants.restrict "condition"
+    (ls: builtins.length ls == 2)
+    (yants.list yants.any);
+
+  /* cond :: [ [ bool any ] ] -> any
+   *
+   * Like the common lisp macro: takes a list
+   * of two elemented lists whose first element
+   * is a boolean. The second element of the
+   * first list that has true as its first
+   * element is returned.
+   *
+   * Example:
+   *
+   * cond [
+   *   [ (builtins.isString true) 12 ]
+   *   [ (3 == 2) 13 ]
+   *   [ true 42 ]
+   * ]
+   *
+   * => 42
+   */
+  cond = conds:
+    if builtins.length conds == 0
+    then builtins.throw "cond: exhausted all conditions"
+    else
+      let
+        c = condition (builtins.head conds);
+      in
+        if builtins.head c
+        then builtins.elemAt c 1
+        else cond (builtins.tail conds);
+
+  # TODO(sterni): condf or magic
+  # like <nixpkgs/pkgs/build-support/coq/extra-lib.nix>
+
+  match = val: matcher: matcher."${val}";
+
+in {
+  inherit
+    cond
+    match
+    ;
+}